This invention generally relates to lubricant compositions for use in diecasting of metals, having improved lubricant and release properties.
Diecasting machines, which include the pressure diecasting and squeeze casting processes, operate under high pressures and temperatures. The faces of the dies must be lubricated and sealed so that the cast metal can flow efficiently and can be released cleanly. In addition, various moving parts must be lubricated. The basic requirements of lubricant compositions for diecasting are as follows: (1) Parting Ability--it must be possible to release the castings from the die surface without distortion or undue stress. (2) Barrier Formation--the lubricant must form a physical barrier between the cast metal and the face of the die in order to reduce adhesion of the cast metal to the die surface (referred to as "soldering" or "galvanizing", depending on the metal being cast). (3) Control of Surface Finish--the lubricant composition must not leave undesirable residues on the die face which might corrode the steel or impair the surface of the casting and hinder or prevent subsequent finishing operations. (4) Soundness of Casting--the lubricant composition must not give off excessive amounts of gas which might lead to porosity of the casting surface and affect the pressure tightness of the castings. (5) Health and Safety--it is important that lubricants do not contain dangerous or toxic components or components which will react to form undesirable byproducts.
In the early days of diecasting, various pastes, oils, greases, and waxes were used and these were applied to the die by various means including brushing. These materials often caused a severe fume problem as solvent and oil evaporated or burned off the hot die surface.
Silicone oils in some instances can be effective release agents, however under most conditions the silicone oils lack sufficient lubricant properties, especially for moving pans. Still further, hydrocarbon oils or polyethylene can cause the buildup of degradation products on the die faces and on the exterior of the dies. Buildup on the die faces themselves leads to inferior casting and surface staining, and shortens the overall life of the die. Deposits on the outside of the die can be troublesome and difficult to remove, requiring mechanical abrasion in the absence of effective solvents. Build up on the mating surfaces of dies can prevent complete closure of the dies, leading to dimensional inaccuracies of the castings.
There has thus been a need in the art for an improved lubricant/release agent which has the appropriate surface active properties to "wet" the die surface, suitable viscosity ranges to flow evenly, but stay in place on the die surface during the casting operation, while at the same time being suitably fugitive or removable so as to provide clean castings and die surfaces.